Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.59   13.806%   $214.6267   $214.63   $214.65   $214.60  
  Purchase #2 $203.47   8.543%   $220.8524   $220.85   $220.85   $220.90  
  Purchase #3 $152.86   3.256%   $157.8371   $157.84   $157.85   $157.80  
  Purchase #4 $51.71   13.707%   $58.7979   $58.80   $58.80   $58.80  
  Purchase #5 $212.82   4.367%   $222.1138   $222.11   $222.10   $222.10  
  Purchase #6 $224.88   8.107%   $243.111   $243.11   $243.10   $243.10  
  Purchase #7 $119.29   13.443%   $135.3262   $135.33   $135.35   $135.30  
  7 purchase totals = $1,153.62       $1,252.6651   $1,252.67   $1,252.70   $1,252.60